In this study, an integrated monitoring and evaluation approach was proposed to fix the systematic safeguarding gap of the Great Wall corridor using space technologies. Two representative sections of the Great Wall located in Qingtongxia County and Zhangjiakou City in China were selected for a preliminary comparative investigation to ascertain the coupling mechanism and spatiotemporal characteristics of the driving forces for the heritage damage. The surface deformation rates were estimated by synthetic aperture radar interferometry, and the interaction between the deformation rates and the normalized difference vegetation index (NDVI) and meteorological and topographic data was calculated using the correlation matrix. The results showed the following: 1) the surface motions along the observed landscape corridor of the Great Wall were decreased in 2015-2018; 2) the correlation coefficients between the deformation rate and the elevation, slope, annual wind speed, and NDVI in Qingtongxia were 0.524, 0.115, 0.582, and 0.522, respectively, indicating the dominant influence of surface runoff and high winds on the degradation of the rammed-earth wall in the western arid regions; vice versa, 3) the correlation coefficients between the deformation rate and the aforementioned factors in Zhangjiakou were 0.065, 0.027, 0.025, and 0.052, respectively, indicating negligible effects of natural processes for the decline of Great Wall in the eastern section. This study not only provides new insights into preventive monitoring and risk assessment of the entire Great Wall but also highlights the potential of space technologies and a geographical perspective for the sustainable conservation of large-scale heritage sites.
The Great Wall of China is one of the largest architectural heritage sites globally, and its sustainability is a significant concern. However, its large extent and diverse characteristics are challenges for deformation monitoring. In this study, the Shanhaiguan section of the Great Wall was investigated in a case study to ascertain the damage and potential hazards of the architectural site. Two standard multi-temporal synthetic aperture radar interferometry (MTInSAR) technologies, including persistent scatterer SAR interferometry (PSInSAR) and small baseline subset (SBAS) SAR interferometry, were used for deformation monitoring using high-resolution TerraSAR-X data acquired in 2015–2017. The results of the two MTInSAR approaches reveal the health condition of the Great Wall. The Shanhaiguan section was stable, but local instabilities caused by rock falls were detected in some mountainous areas. In addition, the applicability of PSInSAR and SBAS was evaluated. The performance analysis of the two approaches indicated that a more reliable and adaptable MTInSAR technique needs to be developed for monitoring the Great Wall. This study demonstrates the potential of MTInSAR technology with high-resolution data for the health diagnosis of heritage sites with a linear structure, such as the Great Wall.
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